This invention is directed to an apparatus and method for casting molten refractory and particularly to the very rapid chilling of molten aluminous abrasive such as the alumina-zirconia abrasives of the type described in the Rowse and Watson U.S. Pat. No. 3,891,408. In casting such molten alumina-zirconia abrasives it is highly desirable that the product be cast in a very thin layer so as to achieve the extremely rapid freezing of the abrasive under controlled conditions that inhibit the oxidation of the product as it is being cooled to a stable temperature. This provides extremely small crystal size, and where an alumina-zirconia eutectic is present, provides extremely small spacing between the zirconia rods and platelets in the eutectic mixture. It also provides for a high "tetragonal" zirconia content in the resultant crystalline structure. It is also believed that a substantial content of reduction products is helpful in these alumina-zirconia abrasives. While the exact function of these reduction products (either sub-oxides or metallic inclusions) is not fully understood, it is believed that they provide an improved performance for many types of grinding.
Whatever the function of the reduction products it is desired to preserve them and accordingly it is a principal object of the present invention to provide a method and apparatus which will give extremely rapid cooling of very thin sheets of molten abrasive.
A further object of the invention is to provide such method and apparatus which will protect the cooling abrasive from contact with an oxidizing environment until the temperature thereof has been reduced to below red heat, at which point the chilled abrasive can be safely exposed to oxidizing atmospheres such as the air and water for removing the final sensible heat therefrom without there being any harmful oxidizing reaction taking place that would detract from the properties desired in the final product.